A LCD (Liquid Crystal Display) apparatus which is installed in a personal computer, a mobile phone or the like includes a liquid crystal display panel in which a liquid crystal layer is sandwiched between two substrates and includes a backlight arranged behind the liquid crystal display panel.
As a light source of the backlight, a linear light source such as a CCFL (Cold Cathode Fluorescent Lamp) or the like is used, as disclosed in Japan patent application publication number 2001-108988 (hereinafter, referred to as document 1). However, the CCFL includes a disadvantage in color reproduction range. Therefore, a backlight which employs a LED as the light source is used increasingly in recent years.
When a LED is applied to a light source for a medium-sized or a large-sized display apparatus, a large number of LEDs are needed in order to generate required brightness Furthermore, in order to generate a white light, a plurality of LEDs including a LED emitting a red light, a LED emitting a green light, and a LED emitting a blue light have to be used.
If LEDs emitting red, green and blue lights are employed as the light source for the backlight, the red, green and blue lights have to be homogeneously mixed. Moreover, the mixed lights have to be emitted toward a display face as an even light. Therefore, the backlight requires a second light guide plate for mixing lights having three colors in addition to a first light guide plate for illuminating the mixed lights. An example of the liquid crystal display apparatus which uses the above mentioned LEDs as the light source is disclosed in Japan patent application publication number 2004-199967 (hereinafter, referred to as document 2). FIG. 42 is a cross sectional view showing a configuration of the liquid crystal display apparatus.
As shown in FIG. 42, the liquid crystal display apparatus includes a liquid crystal display panel 39 and a light source apparatus which illuminates the liquid crystal display panel 39. The light source apparatus mainly includes a LED 31 as a light source, a first light guide plate 37 and a second light guide plate 33. One end face of the second light guide plate 33 receives a light emitted from the LED 31. Then, the second light guide plate 33 mixes the received light therein and emits the mixed light, that is, a white light from other end face. Afterward, the first light guide plate 37 receives the light emitted from the second light guide plate 33 and emits the light from a whole main surface thereof. The light emitted from the first light guide plate 37 illuminates the liquid crystal display panel 39. The LED 31 and a first reflector 32 are mounted near an incident face of the second light guide plate 33. The LED 31 includes a LED emitting a red (R) light, a LED emitting a green (G) light and a LED emitting a blue (B) light.
The first reflector 32 reflects the light emitted from the LED 31 to guide the light to the second light guide plate 33. A second reflector 34 is mounted on a side of an emission face of the second light guide plate 33. The second reflector 34 reflects the light to an incident face of the first light guide plate 37. The second reflector 34 encircles the emission face of the second light guide plate 33 and a side face of the first light guide plate 37. In order to reflect the light efficiently, the first reflector 32 and the second reflector 34 include a mirror face on each of inside surfaces. The liquid crystal display panel 39 is mounted on a side of the display face of the first light guide plate 37. An optical sheet 38 is arranged between the first light guide plate 37 and the liquid crystal display panel 39. The optical sheet 38 includes a diffusion sheet, a protection sheet and a prism sheet. The optical sheet 38 diffuses or concentrates an incident light which is emitted from the first light guide plate 37 and inputted to the optical sheet 38. Afterward, the optical sheet 38 emits the light toward the liquid crystal display panel 39.
A reflection sheet 36 is arranged on a side of a rear side (a side away from the liquid crystal display panel 39) of the first light guide plate 37. The reflection sheet 36 reflects a light emitted from a bottom face of the first light guide plate 37 and emits again the reflected light to the first light guide plate 37. That is, the reflection sheet 36 is used in order to improve use efficiency of the light in the first light guide plate 37.
Next, light propagation in the liquid crystal display apparatus will be described with reference to FIG. 42. Lights emitted by the LED 31 is directly inputted to the incident face of the second light guide plate 33 or is inputted to the incident face thereof by reflection by the first reflector 32. The lights inputted to the incident face of the second light guide plate 33 is mixed while propagating in the second light guide plate 33. The lights are fully mixed and become a white light. The white light is emitted from the emission face of the second light guide plate 33 and inputted to the second reflector 34. The second reflector 34 reflects the light emitted from the second light guide plate 33 toward the first light guide plate 37. The light inputted into the first light guide plate 37 diffuses in whole of the first light guide plate 37 homogeneously. After that, the diffused light is emitted from the emission face (illumination face) which faces the optical sheet 38 and the liquid crystal display panel 39. The Light emitted from a rear face of the first light guide plate 37 is reflected by the reflection sheet 36. The reflected light is inputted into the first light guide plate 37 again.